portico: Change CSS class to float-left and float-right.

This is done because the current column-left and column-right were
actually just floating left and right and making use of float-left
and float-right makes more sense. This also helps with the upcoming
public archives feature which will try to include portico content
with main app content.

static/html/5xx.html

@@ -19,7 +19,7 @@
         <!-- so we can't use variables -->
         <div class="header" style="background-color: #c9e9e0;">
             <div class="header-main" id="top_navbar">
-                <div class="column-left">
+                <div class="float-left">
                     <div>
                         <a class="brand logo" href="https://zulipchat.com/">
                             <svg class="brand-logo" xmlns:svg="http://www.w3.org/2000/svg" xmlns="http://www.w3.org/2000/svg" width="100%" height="100%" viewBox="0 0 40 40" version="1.1">

static/styles/portico.css

@@ -1347,14 +1347,6 @@ input.new-organization-button {
     margin-right: 5px;
 }
 
-.column-left {
-    float: left;
-}
-
-.column-right {
-    float: right;
-}
-
 .top-links {
     text-align: right;
 }

templates/zerver/portico-header.html

@@ -1,6 +1,6 @@
 <div class="header portico-header">
     <div class="header-main" id="top_navbar">
-        <div class="column-left">
+        <div class="float-left">
             <div>
                 {% if custom_logo_url %}
                 <a class="brand logo" href="{{ root_domain_uri }}/"><img draggable="false" src="{{ custom_logo_url }}" class="portico-logo" alt="{{ _('Zulip') }}" content="Zulip" /></a>
@@ -24,7 +24,7 @@
             </div>
         </div>
 
-        <div class="column-right top-links">
+        <div class="float-right top-links">
             {% if user_is_authenticated %}
                 {% include 'zerver/portico-header-dropdown.html' %}
             {% else %}